I use Goggles... Scott Sequence. I can't explain why, but I can, for the most part, ride through snow with them on and not have to do anything. I don't even have to wipe them off, or at least only very seldom. Even with a balaclava on, they don't get fogged. If I have two balaclavas on, with both over my mouth and nose, they'll fog, but I don't do that anyway because it doesn't let me breathe well. If the cold is that extreme I simply wear one of the balaclavas around my face and nose.

Get some good goggles that are fog resistant. The Scott brand seems to be excellent.